Apparatus for forming electrostatic printing heads



C. R. JOYCE April 5, 1960 APPARATUS FOR FORMINGELECTROSTATIC PRINTING HEADS 2 Sheets-Sheet 1 Filed D90. 28, 1956 INVENTOR.

CEQIL R. JOYCE AGENT C. R. JOYCE April 5, 1960 APPARATUS FOR FORMING ELECTROSTATIC PRINTING HEADS Filed Dec. 28, 1956 2 Sheets-Sheet 2 INVENTOR.

cecu. RY' JOYCE AGENT APPARATUS FOR FORMING ELECTROSTATIC PRINTING HEADS Cecil R. Eoyce, Paoli, Pa., assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Application December 28, 1956, Serial No. 631,194

9 Claims. (Cl. 18-36) The present invention relates to electrostatic printing and more particularly to a novel apparatus for forming electrostatic printing head assemblies having an array of electrodes for printing or plotting data upon a suitable responsive medium.

In the development of electrostatic printing, efiective results largely depend upon complicated circuits for character selection requiring a multiplicity of printing electrodes. Heretofore, and particularly where commercial production is concerned, the problem of properly arranging, separating and mounting such electrodes has introduced a prohibitive cost factor which has seriously retarded efforts to meet the trade demands for such equipment.

The important object of the present invention is to provide a novel apparatus for forming electrostatic recording and printing heads wherein the heretofore high cost of such devices has been substantially reduced.

A further object is to provide such apparatus making it possible to form two such electrostatic heads simultaneously.

In accordance with the above objects and first briefly described the invention comprises apparatus whereby a plurality of electrode-forming conductive wires may be positioned through a box mold under tension and substantially parallel with and spaced from each other and the walls of the mold, and with separated groups of the wires stacked in substantially parallel planes, and whereby those portions of the wires extending through the mold may be imbedded in a molding material by filling the box with the material. After the material has set the unit is removed from the mold box and severed along a line transversely to the direction of the wires thus to form the molded body into two heads simultaneously.

Fig. l is a side elevation view of a jig or molding frame, with one side removed to show the wire positioning elements, and with parts broken away;

Fig. 2 is an end elevation of the same;

Fig. 3 is a detail view of a wire positioning cylinder;

Fig. 4 is a section view on line 44 of Fig. 1;

Fig. 5 is a perspective view of the head as removed from the mold;

Fig. 6 is an exploded view of the two heads formed by dividing the head of Fig. 5;

Fig. 7 is a face view of a molding jig for the completed head and lead wires; and

Fig. 8 is a face view of the completed head unit as removed from the jig of Fig. 7.

Referring to the drawings, one form of apparatus for fabricating the head assembly comprises an elongated open top box frame 10 having two spaced apart transverse partitions 11 forming the ends of a form to receive a chemically exothermic molding material, such as epoxy resin, for embedding conducting wires 12 terminating at one end respectively in the pattern or array of electrodes as a printing head and at the other end in a plurality of connecting leads when the manufacturing steps are completed. Each partition 11 is provided with an open I 2,931,065 Patented Apr. 5, 1961) top slot 13 through which the wires are positioned. A

body of grease 14, such as Dow Corning silicone grease dams the ends of slots 13 to retain the molding material when poured.

For positioning wires 12 for the molding operation, two rows 15 of cylinders, preferably of brass, are transversely disposed between the extended sides of the box 10 on the outer sides of partitions 11. Each cylinder has its opposite ends seated on support strips 16 which are fixed to the box sides by screws 17 so that all supporting surfaces lie in the same horizontal plane. In the illustrative form of the invention there are five cylinders numbered 18, 19, 20, 21 and 22 in one row, and five cylinders numbered 23, 24, 25, 26 and 27 in the other row. The specific number of cylinders in each row is for the purpose of making the selected head array of five superposed spaced transverse rows of electrodes with, in this instance, seven lineally disposed electrodes in each row, see Fig. 4.

In order to properly space wires 12, each cylinder of the two alined rows is formed with seven circumferential V-shaped grooves 28, respectively alined in pairs, that is, each groove of each cylinder row lies in the plane of the groove in the corresponding cylinder of the other row. Since the pattern selected here is formed by five rows of wires spaced one above the other with seven wires to a row. provision has to be made for arranging the row planes properly spaced apart and this has been accomplished by successively increasing the diameter of the cylinders in graded relation. Thus, the first pair of cylinders 22 and 23 are of the same diameter; the second pair of cylinders 21 and 24, while of the same diameter, have a larger diameter than the first pair; the third pair of cylinders 20 and 25, while of the same diameter, have a larger diameter than the second pair of cylinders; the fourth pair of cylinders 19 and 26, while of the same diameter, have a larger diameter than the third pair; the fifth pair of cylinders 18 and 26, while of the same diameter, have a larger diameter than the fourth pair. This graded difference of cylinder diameter, in the present instance, is of the order of seventeen-thousandths of an inch. Thus, the five planes of wires 12, when seated in the respective pairs of grooves and placed under tension, are vertically spaced apart illustratively by predetermined thousandths of an inch.

In order to ensure accurate alinement of the linear rows of grooves 28, by precision positioning of the cylinders, the inner face 311 of one of the sides of frame 10, ismachined as a true plane as areference against which the planar end of each cylinder abuts. Each cylinder is anchored in its abutting position by an adjusting screw 31 threaded through the opposite side of the frame 11) to axially press against the end of the cylinder to which it is associated. Thus when all of the cylinders have been anchored, all of the individual grooves 28 of the mating similar sized cylinders lie in parallel planes.

For placing the rows of wires 12 under tension, frame 10 is mounted upon a bridge piece 32 carrying depending diverging plates 33 nad 34 at opposite sides respectively with each plate below a row of cylinders, to properlylocate spring tensioning units for the respective wires.'

The tension assembly on plate 33 comprises transverse rows of pins 35 upstanding from the face of the plate:

Each pin serves as an anchor for an end of one Offlinumber of tension springs 36, the other end of which hasa clamp 37 to which one wire 12 is attached. Similarly the tension assembly on plate 34 comprises transverse rows of pins 33 upstanding from the plate face. Each pin serves as an anchor for an end of one of a number of tension springs 40 respectively terminating in clamps 41 to which the ends of wires 12 from springs 36 are individually attached after crossing the mold. In assentbling the planes of wires, the linear set formed with cylinders 22 and 23 will be described in detail as illustrative of the way the wires of all the sets are strung. Initially cylinders 22 and 23 only are in place, but precision anchored against the reference side 30 of frame 10, whereupon one wire 12 is attached to its clamp 37 and brought up over cylinder 22, then across the cavity of the mold and over cylinder 23 for connection to its clamp 41 and held taut by springs 36 and 40. Each of the wires so strung is seated in a pair of alined grooves 28. A second wire 12 is strung in the same way to define the second wire of the set, and thus successively the wires are strung to form a plane of seven wires all in the respective cylinder grooves and lying in the bottom of slots 13 in partitions 11, see Figs. 1 and 4.

For forming the second plane of stretched wires, cylinders 21 and 24 are placed in position abutting cylinders 22 and 23, and anchored against the reference .side of the frame, whereupon wires 12 are strung in taut condition under spring tension to form the second plane of wires spaced from the first plane because of the greater diameter of cylinders 21 and 24. The additional planes of wires are strung in the same manner, it being understood that prior to each stringing operation the proper pairs of cylinders are placed and properly precision anchored to ensure exact alinement of the cylinder grooves.

With all of the wire planes properly arranged in and across frame 10, the cavity of the form is filled with a chemically exothermic material, such as epoxy resin, which is poured in and allowed to set as a solid body 42 (Fig. having the Wire array embedded therethrough with conductors or lead wires 43 projecting from opposite sides. When the molded unit has set it is removed from the mold and, as seen in Fig. 6, divided into two unitary parts 42a and 4% by cutting it medially transversely so that each part forms a head with the predetermined pattern of electrodes 44 exposed at one end surface while from the other end surface leads 43 project to be respectively connected to the terminals of control circuits.

In order to form a complete magnetic head unit from each of the separated head parts, a novel means for connecting the separate leads 43 to external circuit connectors has been devised wherein the present thirty-five leads are insulated one from another by passing each through a tube of insulating material, such as known in the trade as spaghetti. In this way each electrode of the head is continued as a conductor completely isolated electrically from all of the others for respective connection to clips or connectors 46 each of which provides means for joining an external wire to close a control circuit as determined by a selected electrode or electrodes of the head.

As a means for accurately and orderly making the connections between the conductors or leads 43 and the clip 46, while maintaining proper spacing, two strips 47 and 48 are mounted in spaced edge to edge relation upon a base 50 across one end of which the molded head 42a or 42b is removably attached. The thickness of the two strips 47 and 48 preferably corresponds generally to the thickness of the molded head, and are preferably of aluminum having each juxtaposed edge formed with slots 51 corresponding in number to the number of clips 46, which are to be respectively seated therein for convenient soldering of the free ends of the leads 43 thereto. In the present example there are eighteen slots 51 on strip 47 and seventeen slots 51 on'strip 48 to conform compound while the free ends of the clips are protected from the compound and will remain projected from the respective sides of the molded unit when the unit is lifted out of the mold. Cover members 52 are arranged to be clamped in hold-down position by screws 53 or like fastening means. Also an end member 54 is superposed upon the head 43 and fastened by screws 55 straddling head 43 and entering base 50, such end member abutting the adjacent ends of strips 52.

The space between the opposite ends of strips 52 is closed by a transversely disposed block 56 having, in this instance, a medially located lug 57 projecting into the space between the aforesaid strips. As so assembled the parts form a mold jig or frame bounding a cavity in which the two banks of lead conductors 43 lie ready to be embedded in a potting compound, preferably epoxy resin.

After the compound is poured into mold cavity and has set, the hold-down members 52, 54 and 56 are removed and the formed head unit lifted out as a relatively flat plate 58 (Fig. 8) of truncated shape having two rows of clips 46 projecting respectively from two opposite sides thereof and with the printing head at one end. The opposite end of the unit has a slot 60 formed therein as a result of molding about lug 57, such slot '60 serving as an anchoring guide in assembling a plurality of the printing head units.

As a component part the invention includes a novel method wherein a plurality of conducting wires can be arranged in an array or predetermined pattern as a step coordinated with other steps to transform the arrangement into a, printing head having electrodes exposed as a replica of the selected array or predetermined matter. Such steps include arranging the conducting wires in spaced linear relation, maintaining the wires under tension in such relation, pouring an insulating compound about the tensioned wires, permitting the compound to set, removing the unit from the mold, and then severing the compound and wires transversely to form the printing units each with a printing head at one end and a plurality of lead wires projecting from the other end. Severing of head 42 can be made at a location resulting in a single printing head with its pattern of electrodes, or it can be made between the ends of the embedded wires at a location such that two heads are formed by the one operation.

It will now be apparent that the invention provides novel apparatus for forming a printing head having a predetermined pattern of embedded electrodes with lead connections respectively for external control circuits.

What is claimed is:

1. Apparatus for forming electrode printing heads, comprising a box frame having a bottom wall, side walls, and transverse partitions forming end walls, each of said partitions being provided with a recess in its top edge, said recesses being aligned with each other between said side walls, means for positioning a plurality of conducting wires through said recesses in a manner traversing said box frame substantially parallel with and spaced from each other and said side and bottom walls and with separated groups of said wires stacked in substantially parallel transverse planes, said wire posltiornng means comprising a plurality of rigid members successively arranged on the outer side of each of said part1- tions, each member of each group having a top edge portions arranged in a plane substantially parallel with said bottom wall, successive of said edge portionsoutwardly from said partitions being in successively higher positions above said bottom wall and aligned with said recesses, and means for holding said wires under tension to maintain said planar relationship.

2. Apparatusaccording to claim 1 wherein said l'lgld members comprise two rows of rollers, one row on the outer side of each of said partitions, and wherein said top edges are formed by the periphery of said rollers.

3. A construction in accordance with claim 2 and further including means mounting said rollers for limited movement relative to each other and to said partition.

4. Apparatus for forming electrode printing heads, comprising an open top box frame having a bottom wall, spaced apart side walls having portions extending beyond the ends of said bottom wall, and transverse partition forming end walls positioned inwardly of the outer ends of said side wall extensions, each of said end walls being provided with a recess in its top edge, said recesses being aligned between said side walls, means for positioning a plurality of conducting wires through said recesses in a manner traversing said box frame substantially parallel with each other and spaced from said bottom and side walls, said wires being in spaced relation with each other and with separate groups of wires stacked in transverse parallel planes, said last means comprising a plurality of successively aligned elements extending between said side wall extensions on the outer sides of said partitions, each successive element of each plurality from the partitions outwardly having a top edge portion at a successively higher plane above said bottom wall, with the top edge portions of similarly positioned elements from the partitions outwardly being substantially in the same plane, and means for holding said wires over said elements under tension to maintain said planar relationship of said wire groups.

5. Apparatus for forming electrode printing heads, comprising an open top box frame having a bottom wall, spaced apart side walls having portions extending beyond the ends of said bottom wall, and transverse partitions forming end walls at the ends of said bottom wall, each of said end walls being provided with a recess in its top edge, said recesses being aligned between said side walls, means for positioning a plurality of conducting wires through said recesses in a manner traversing said box frame substantially parallel with and spaced from each other and said bottom and side walls, said wires being in separate groups stacked in transverse parallelplanes, said last means comprising two rows of rollers transversely disposed between the extensions of said side walls, one row being positioned on the outer 6 side of each of said partitions, said rollers being of successively larger diameter with the smaller diameter rollers being next to said partitions and positioned with their top surfaces at successively higher planes respectively,

and means beneath said rollers for holding said wires over the periphery of said rollers under tension to maintain said planar relationship of said wire groups.

6. Apparatus in accordance with claim 5 wherein said side wall extensions include rail means adjacent their inner bottom edges for supporting said rollers in rolling engagement therewith and between said side wall extenmom.

7. A construction according to claim 6 and further including means for releasably fixing the position of said rollers relative to said side wall extensions and said partitions.

8. A construction in accordance with claim 5 wherein said holding means comprises a plurality of elements for gripping the opposite ends of said wires, and spring means attaching said last means to fixed structure.

9. A construction in accordance with claim 5 wherein said end wall recesses are dammed up by grease-like material permitting the wires to be inserted through said grease into their planar positions and preventing molding compound poured in said frame around said wires from flowing out of said frame through said recesses.

References Cited in the file of this patent UNITED STATES PATENTS 2,008,162 Waddell July 16, 1935 2,113,674 Brickrnan et a1. Apr. 12, 1938 2,151,292 Brickman et al Mar. 21, 1939 2,402,333 Morehead June 18, 1946 2,500,258 Mazzoni Mar. 14, 1950 2,568,771 Smith Sept. 25, 1951 2,684,503 Silver July 27, 1954 2,685,107 Schultz Aug. 3, 1954 2,726,923 Slhleich Dec. 13, 1955 2,794,211 Brown June 4, 1957 FOREIGN PATENTS r 700,947 Great Britain Dec. 16, 1953 

